1. Field of the Invention
The present invention relates to a coating device and a coating unit in a stencil printing apparatus, and more particularly, to a coating device in a stencil printing apparatus in which the surface of a sheet printed using a stencil printing apparatus is coated with a viscous coating liquid such as a UV-curable varnish or the like, and to a coating unit that is mounted on a printing apparatus main body in place of a detachable printing drum unit.
2. Description of the Related Art
Known simple printing apparatuses include, for instance, digital heat-sensitive stencil printers (hereinafter, simply “stencil printing apparatuses”) for digital heat-sensitive stencil printing. In such stencil printing apparatuses, a thermal head, having a plurality of small heat generators arranged in a main scanning direction, is brought into contact with a thermosensitive stencil master (hereinafter “master”), also called stencil paper, as the master is transported in a sub-scanning direction (master transport direction) that is perpendicular to the main scanning direction, while the heat generators are energized in pulses to thereby heat-melt punch the master in accordance with image information. The perforated master is wrapped around the outer peripheral face of a porous circular plate cylinder that is provided on the outer periphery of a printing drum, whereafter the outer peripheral face of the plate cylinder is pressed by a pressing means such as a press roller or the like, with printing paper (hereinafter also simply “paper”), as the medium to be printed, interposed therebetween. As a result, ink that is supplied to the inner peripheral face of the plate cylinder bleeds from the perforated portion of the plate cylinder and the perforated part of the master, whereupon the ink is transferred to the paper to yield a printed image. The printing drum is also referred to hereinafter as simply “drum”.
The above stencil printing apparatuses, having low running costs and being operable at high speed, are extensively used for printing circulars, forms and the like in, for instance, the education market, but also in public offices, associations, hospitals and so forth, and for printing large runs of newspaper inserts, real estate advertisements, internal memos in private businesses and the like. That is because such inexpensive apparatuses enable easy printing by anyone at any time.
The printing paper used herein is ordinary paper or recycled paper, thus relatively inexpensive, the surface of which exhibits high ink penetration. This makes the images on the surface of the printed product look dull and drab. Also, the print image ink may dry apparently by penetrating into the fibers of the paper. Ordinarily, special fixing devices do not achieve complete fixing, and hence the resulting printed product is inferior from the viewpoint of storability, since rubbing thereof with the fingers may give rise to smears, while the printed product itself may become weakened if wet with water.
Known methods for imparting a stylish feel, as well as storability and abrasion resistance, to such printed products, include, for instance, lamination methods in which a transparent film is affixed to the surface of the printed product. Lamination, however, is time-consuming, and hence a low-productivity method, and is also problematic in that it requires a special device, called laminator, for heat fusion, and in that films are expensive.
Meanwhile, varnish coating devices are also known for imparting a stylish feel, as well as storability and abrasion resistance, to printed products. Varnish coating devices are dedicated devices for applying a transparent varnish on the surface of the printed product while the latter is being transported. Such devices are relatively bulky and expensive, and hence varnish coating was not something that could be done by anyone, readily and inexpensively.
Conventional varnish coaters are full-fledge coaters in which varnish is often applied over the entire surface of the printed product. These coaters are thus large equipment items that are used in printing establishments. Given that such equipment is large, expensive and requires trained personnel for its operation, no equipment has been known thus far that allows the user him/herself to coat with varnish an ordinary printed product, easily and quickly. Moreover, after coating the entire surface of the printed product with varnish, the periphery of the printed product is cut off. This requires an expensive dedicated paper cutter, which only printing establishments can afford.
Specifically, Japanese Patent Application Laid-open No. 2007-111873 (Prior Art 1) and 2006-76080 (Prior Art 2) disclose water-based varnish coating devices in large offset printing apparatuses.
Also, Japanese Patent Application Laid-open No. 2006-35816 (Prior Art 3) discloses a relatively small-size independent dedicated varnish coating device.
Japanese Patent Application Laid-open No. 2004-313829 (Prior Art 4) discloses a varnish coating device and a printer, in which a UV-curable varnish is sprayed, by liquid spraying nozzles, onto a specific area of printing paper, followed by curing through UV irradiation.
Since the above-described digital stencil printing apparatuses enable easy printing by anyone, inexpensively and by way of a simple operation, they are also widely used by free operators for printing relatively small runs. Japanese Patent Application Laid-open No. 2006-281711 (Prior Art 5) describes such a stencil printing apparatus, having a plurality of printing drum units that can be detachably mounted on the main body of the stencil printing apparatus, wherein a UV-radiating unit can be mounted in the place of a printing drum unit holding ordinary ink, when a printing drum unit holding a UV-curable ink is mounted upstream of a paper transport direction.
The water-based varnish coating devices disclosed in Prior Art 1 and Prior Art 2, however, are bulky and expensive, and hence not suitable for ordinary users. The varnish coating device of Prior Art 3 is relatively small, but is likewise expensive and unsuitable for ordinary users. Similarly, the varnish coating device of Prior Art 4 is costly and inappropriate for ordinary users.
Stencil printing apparatuses have involved heretofore mainly black printing on ordinary paper, plus occasional use for color printing in red or blue. The above-described drawbacks of inferior storability and poor aesthetics of the surface of printed products obtained in a stencil printing apparatus have become a stereotype, and hence the use of a stencil printing for varnish coating has been deemed unfeasible, or in other words, few considered the potential worth of using varnish coating.